The present invention relates to a method for making a lithographic printing plate and in particular to a method for making a silver salt lithographic printing plate of high sensitivity and high printing endurance by scanner-exposure.
It has been known for a long time to make a lithographic printing plate directly from originals utilizing the high sensitivity of silver halide emulsion and the most popular now is utilization of silver complex diffusion transfer process. (For example, Japanese Patent Kokoku No. 48-30562 and Japanese Patent Kokai Nos. 53-21602, 54-103104 and 56-9750). Recently, there have been developed and begun to be practically used lithographic printing plates which are made utilizing silver complex diffusion transfer process by scanner-exposing using helium-neon laser, argon laser, light emitting diode (LED), semiconductor laser, etc. (For example, Japanese Patent Kokai Nos. 59-71055, 59-71056, 60-29751, 60-19141, 60-100147, 62-103649, and 62-105147-105150).
However, although these lithographic printing plates made by scanner-exposing process have far higher sensitivity than those made by camera-exposing process, they are still not sufficient in the sensitivity and have the defects of low printing endurance, especially, of very fine line images.